v2.4.1.9

Short Term Investments - Additional Information (Detail) (US Treasury Securities, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Investment [Line Items]
Held to maturity securities, amortized cost	198.5us-gaap_HeldToMaturitySecuritiesAmortizedCostBeforeOtherThanTemporaryImpairment	$ 137.2us-gaap_HeldToMaturitySecuritiesAmortizedCostBeforeOtherThanTemporaryImpairment
Held to maturity securities, carrying value	198.5us-gaap_HeldToMaturitySecurities	137.2us-gaap_HeldToMaturitySecurities
Held to maturity securities, fair value	198.5us-gaap_HeldToMaturitySecuritiesFairValue	$ 137.2us-gaap_HeldToMaturitySecuritiesFairValue
Minimum
Investment [Line Items]
Held to maturity securities maturity range	3 months
Maximum
Investment [Line Items]
Held to maturity securities maturity range	1 year

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The stated maturity date of held-to-maturity investments.

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- Definition

Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

+ References

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-Publisher FASB

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-Section 50

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Amount before other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Fair value of investments in debt securities classified as held-to-maturity.

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